The vent to the roof can be any length, it just needs to be sized appropriately for the maximum flow. Whether you can tie into the existing vent instead of making a new penetration of the roof would depend on how close that vent was to the maximum. On the waste side, as long as the pipes can be sloped down to the sump at 1/4"/foot, it should work.
If you connect to an existing vent, it must be above the water line of the highest fixture vented by that line. The waste must be pumped to the sewer line.